The present invention relates generally to a method for applying and delivering pesticides, insecticides, and repellents to structures, surfaces of structures, and materials important to commerce and industry, and more particularly to polyurethane polymer systems containing pesticide(s) and or pellets containing bioactive active chemicals having extremely long useful lives.
Wood and wood products utilized in a variety of construction applications are frequently structurally degraded by the action of termites, ants, other boring insects, and wood decaying microorganisms. Typically, these wood degrading and decaying organisms migrate to wood structures via the surrounding soil or water. This migration may occur whether the structures rest upon concrete foundations, such as in wooden building construction; are in direct contact with the soil, for example fence posts, utility poles, railroad cross-ties, wooden supports, and like structures; or are in the water, such as boats, piers, pier pilings, wooden docks, or other supports. Wood and wood-containing products include, inter alia, glued wood products such as, for example, plywood, particleboard, oriented strand board (OSB), medium density fiberboard (MDF), laminated veneer lumber (LVL), laminated beams, and a variety of other engineered wood products. Paper products (especially paperboard and kraft paper) also are subject to degradation by organisms that attack wood. Outdoor furniture also is subject to wood degrading and decaying organisms. In the marine context (including for example, pleasure and commercial craft for use on lakes and oceans), the structures additionally may be manufactured from fiberglass, various plastics, metals, ceramics, and other materials.
Present methods of preventing or retarding the advance of these wood degrading organisms include soil treatment with pesticides and repellent chemicals, treatment of the wood with chemicals, and fumigation wherein the entire structure may be sealed and a pesticide pest repellent released. Both soil and fumigation type treatments may release the pesticide to the surrounding atmosphere and/or the pesticide may move to ground water where it may harm human beings or other living organisms. Disadvantages of these methods of treating soil and/or fumigating include, inter alia, potential ecological and human health concerns, as well as the limited time until the fumigant or soil concentration is sufficiently reduced in concentration to permit ingress of wood degrading organisms.
Although many pesticides and repellents are known to be effective against the action of wood destroying organisms, their effectiveness often declines over time as they are dissipated into the surrounding environment (soil, water, or atmosphere) or are degraded, for example, chemically or biologically. To retain their effectiveness, these insecticides must be repeatedly applied at regular intervals ranging from every few days to every few months to every few years. Alternatively, if the pesticides and repellents are applied in sufficient quantity to be effective over an extended period of time, the ecological and human health related concerns associated with these chemicals and their unpleasant odors are exacerbated. Furthermore, with the banning of certain chemicals and the introduction of safer shorter half-life compounds, even large amounts of many of these pesticides and repellents may be required over a relatively short time periods, and they will need to be reapplied more often.
A further disadvantage of conventional application methods is that the concentration of pesticides and repellents resulting from a single application starts out well above the minimum concentration necessary for effectiveness, but decreases rapidly. Within a relatively short period of time the concentration drops below the minimal effective level necessary to maintain a barrier to the invasion of wood compromising organisms.
To overcome these problems, a number of techniques for the controlled release of chemicals, such as insecticides, have been proposed. These methods employ polymer matrices and microcapsules used to contain insecticide and allow the slow release of the pesticides and repellents over extended time periods. One such scheme is found in U.S. Pat. No. 4,400,374, which discloses the use of polymer matrices generally made of polyethylene, polypropylene, ethylene vinyl acetate, polyamide, polystyrene, polyvinyl acetate, or polyurethane to control the release of insecticides such as the insecticide commercially available under the trade name DURSBAN. The polymer matrices disclosed in U.S. Pat. No. 4,400,374, incorporate a porosigen and a porosity reducing agent, which upon contact with soil moisture or an aqueous environment dissolves the matrix. Similarly, U.S. Pat. No. 4,405,360 proposes a polymer release matrix, which can be composed of polyamide, polyurethane, polyethylene, polypropylene, polystyrenes, or other polymers. The control release mechanism works in combination with a porosigen to release a herbicide in a moist environment. A disadvantage of both of these methods is the necessity of sufficient moisture to dissolve the matrix. Periods of dryness, while extending the life of the matrix, results in a decrease in the insecticide concentration, thereby permitting insects to have access to the wooden structure. In addition, the longevity of the matrix is variable and dependent upon moisture content.
U.S. Pat. No. 4,435,383 proposes the use of a controlled release mechanism for insecticides including carbamates, organothiophosphates, organophosphates, perchlorinated organics, and synthetic pyrethroids. The release mechanism comprises a hydrophobic barrier that is a polymer prepared from styrene and/or methyl styrene in combination with a monomer selected from one or more unsaturated mono- or di-carboxylic acids. U.S. Pat. No. 5,860,266 proposes the preparation of construction sites with plastic sheets impregnated with an insecticide.
U.S. Pat. No. 4,282,209 proposes a process for the preparation of insecticide-polymer particles. The insecticide, methomyl, is used to control insects, which attack tobacco, cotton, or other agricultural crops. Methomyl is dissolved into polymers, such as polyamides, urethanes, or epoxies, to provide extended residual insecticidal activity. U.S. Pat. No. 4,235,872 proposes the use of slow-release insecticide microcapsules having a core of methomyl surrounded by a cover of all-aromatic, un-crosslinked polyurea to protect vegetables, field crops, and fruit crops.
U.S. Pat. No. 4,198,441 proposes the use of insecticides, such as chlorpyrofos (DURSBAN) in a controlled release matrix comprising an organopolysiloxane, a hydrolyzable silane, and a hydrolyzable organic titanium compound. U.S. Pat. No. 4,160,335 proposes a mode of dispersing insect control substances by applying stripes to sheets of cellophane. The insect control substance, which can include DURSBAN, is placed in a polymer as well.
Australian patent AU-B-82443/91 proposes to use two sheets of plastic drawn from supply rolls, wherein the upper face of the lower sheet and the lower face of the upper sheet are drawn past respective coating rollers which apply a coating of pesticide (e.g., permethrin) in a volatile solvent to the faces of the sheets. The coated faces of the sheets are brought together by passing them between compressive rollers. The coated and pressed sheets are laid under building foundations or placed around trees or plants to prevent termite attack. Disadvantages of this product and method include (1) delamination permits rapid escape of the coating, and (2) the coating is not integral to the sheets, thereby permitting faster diffusion through the sheets and limiting the effective life.
Coated granules have a pesticide absorbed onto a matrix, such as clay, and then coated with cross-linked resins which helps slow the release rate. Clay loses or releases pesticide over a short period of at most a few weeks.
In U.S. Pat. No. 5,801,194, a controlled release device is disclosed, which incorporates insecticide into polymer materials to form a device, which then may be placed in and around wooden structures to form an effective exclusion zone lasting several years or more. The reported extended effectiveness is accomplished by using of low volatility insecticide within a high-density polymer, the combination having a low release rate of the insecticide. While the '194 patent does describe a device that provides long lasting protection against insect penetration, the application of this device to either new or existing structures requires the manual placement of the device in and around those structures. The application of the device in this manner may be time consuming, labor intensive, and expensive. In one embodiment of the '194 patent, the controlled release device is placed into a polyurethane foam to allow the spray application of the device to wooden structures. While this approach does lessen the labor, and thus the cost associated with placing the device in contact with the structures that need to be protected, it does have other drawbacks. For example, at the time the device is applied to the structure, the insecticide is not adequately dispersed throughout the volume of the polyurethane foam. This results in a lack of protection from invasive insects during the time period required for the insecticide to permeate the polymer and infiltrate the foam. To overcome this drawback, the '194 patent also proposes combining the low volatility insecticide within a high-density polymer with a more volatile insecticide within a low-density polymer which has a higher release rate. The drawbacks of this combined system include the potential harm to human and other life forms, which may occur as a result of their coming into contact with the more volatile insecticide.
Japanese 62236937 proposes the use of a polyol/isocyanate/pesticide/microparticle solution that is painted or sprayed upon the surface of the foundation and the ground around the foundation. Inclusion of the microparticles creates gaps between the particles. The gaps are filled with the pesticide containing urethane polymer. Therefore, the urethane polymer containing the microparticles acts as a sponge and enables the release of the pesticide without trapping it. By the varying of the amount of microparticles, the applicator can change the rate of the pesticide release.
Thus, there exists a need for improved pesticide control agents for protecting wooden structures, which improved control agents provide immediate, as well as long lasting, protection from, inter alia, termites, ants, wood boring insects, and other wood destroying microorganisms. It is to such improved pesticide control agents that the present invention is addressed.